Transmission apparatuses such as router apparatuses or wavelength division multiplexing (WDM) apparatuses can be used as an apparatus which transmits information to broadband lines which can be used in rapid communication regarding large capacity information. A plurality of signal processing substrates in which an arithmetic element such as an LSI or a storage element such as a memory is incorporated are installed in the transmission apparatuses for interconnection between each line.
A circuit to which an arithmetic element or a storage element is connected through electric wirings is constructed in each signal processing substrate, but in recent years, transmission of information with higher throughput is required in each substrate according to an increase in the amount of information to be processed. However, when information transmission is rapidly performed, it actualizes problems such as occurrence of crosstalk, generation of high-frequency noise or degradation of electrical signals. Accordingly, electric wirings become a bottleneck and it is difficult to improve throughput of the signal processing substrates. In addition, the same problem occurs even in a super computer or a large-scale server.
Therefore, the above-mentioned problems are investigated to be solved by photonic technology. Optical fibers or optical waveguides which lead optical signals from one point to another point are used in photonic technology. The optical waveguide includes a linear core and a cladding which is provided to cover the surrounding of the core, the core is configured with a substantially transparent material with respect to optical signals, and the cladding is configured with a material having a lower refractive index than that of the core.
A light-emitting element such as a semiconductor laser is disposed on an incidence side of the optical waveguide and a light-receiving element such as a photodiode is disposed on an emission side thereof. Light incident from the light-emitting element is transmitted to the optical waveguide, received by the light-receiving element, and communication is performed based on a blinking pattern or a strong-weak pattern of the received light.
The above-mentioned problem of the electric wiring is solved by replacing the electric wiring in the signal processing substrate with the optical waveguide, and it is expected that the throughput of the signal processing substrate is further increased.
In a case of replacing the electric wiring with the optical waveguide, it is necessary to perform mutual conversion between an electric signal and an optical signal, and accordingly, an optical module including a light-emitting element, a light-receiving element, and an optical waveguide which optically connects the elements to each other is used.
PTL 1, for example, discloses an optical interface including a printed substrate, a light-emitting element which is mounted on the printed substrate, and an optical waveguide which is provided on a lower surface side of the printed substrate. The optical waveguide and the light-emitting element are optically connected to each other through a through hole which is a penetration hole formed in the printed substrate for transmitting the optical signal.
However, a transmission direction of the optical signal is basically limited to one direction in the optical waveguide. Accordingly, in order to perform bidirectional communication in an optical module, it is necessary that individual optical waveguides be prepared for both directions and the light-emitting element and the light-receiving element be disposed together on end portions thereof. In addition, it is necessary that a driver element for driving a light-emitting element or a signal amplification element for amplifying a signal received by the light-receiving element be disposed to be close to the light-emitting element or the light-receiving element.
When the elements are disposed to be close to the above-mentioned elements and an arithmetic element such as an LSI is disposed to be close thereto, high speed and large-capacity data transmission and reception using optical communication can be performed between the arithmetic element mounted on the optical module and the arithmetic element mounted on another module.